Diphenhydramine in asthma: what to know

Diphenhydramine is an antihistamine used for symptoms such as sneezing, an itchy nose or hives. It does not open narrowed airways or control the inflammation that drives asthma. It can also cause drowsiness, dry mouth and slower reactions. Some combination cold or allergy products contain it, so check labels before taking more than one product.

Allergic rhinitis or house dust mite allergy can occur alongside asthma, and controlling nasal allergy may reduce an individual’s triggers. It should not be used as a substitute for an inhaler prescribed for asthma. Cough, wheezing or chest tightness need to be considered as asthma symptoms, not simply treated as allergy.

Continue your prescribed asthma plan and use medicines exactly as directed. Before taking diphenhydramine, ask a pharmacist or clinician to check the product, especially if you use other medicines that cause sleepiness, have glaucoma, prostate problems or breathing concerns. Avoid driving or alcohol if it makes you drowsy. Keep a record of the symptom being treated and whether breathing changes after taking it.

If symptoms follow an allergen, move away from the trigger where possible. Do not delay your prescribed reliever while waiting for an antihistamine to work. A nebuliser treatment may be considered by clinicians in particular situations, but home treatment should follow your written plan.

Seek urgent medical help if breathing is rapidly worsening, you cannot speak comfortably because of breathlessness, your lips look blue or grey, you feel faint, or your reliever is not helping as your action plan expects. Severe chest tightness or wheezing after a medicine may indicate a serious reaction and needs prompt assessment.

Ask whether your symptoms fit allergy, asthma or both; whether diphenhydramine is appropriate with your inhalers; and how to recognise a flare that needs urgent care.